1. Field of the Invention
This invention relates generally to electronic test instruments, and more particularly to a method and apparatus for precisely locating fault conditions in electrical cable harnesses, electronic interface cables and the like having a variety of configurations such as combinations of individual conductors, twisted wire pairs, coaxial cables, individual or multiconductor shielded wires, etc. As employed herein fault conditions include short circuits, high impedance leakage paths up to about 100 megohms and open circuits.
2. The Prior Art
Electrical cable harnesses and electronic interface cables are generally encased in some form of protective sheathing or sleeving, and for use in demanding environments these cables are typically potted or waterproofed. Other types of cables may often be either buried underground or suspended above the ground from poles or towers. Fault conditions sometimes develop requiring repair of the cables or replacement of the faulty portions thereof. As the lengths of cable under investigation may be quite long, for example of the order of hundreds or even thousands of feet, and the fault condition to be located may be anywhere in the entire length, it is important that the fault condition be accurately located. This is especially true in the case of underground cables where a hole must be generally dug to permit access to the faulty portion of the cable.
Known apparatus and methods for locating fault conditions are shown in U.S. Pat. Nos. 3,800,216 to Hamilton and entitled "Cable Fault Locator Apparatus And Method With Reference Voltage Comparison;" 2,551,942 to Greene and entitled "Apparatus For Locating Faults In Electric Circuits;" 2,120,391 to Butterfield and entitled "Measuring Device;" and 1,958,361 to Estes et al. and entitled "Method Of Locating Faults In Cable Conductors." However, these known apparatus and methods have several shortcomings such as being applicable to only one type of fault condition, e.g. short circuits, or requiring manual balancing of circuits and undesirably complicated determinations on the part of unskilled linemen or repairmen.
It is an object of this invention to provide an apparatus and method for rapidly and automatically measuring the length of a cable to be tested and determining the precise location of a fault condition in the cable without requiring undesirably complicated determinations by unskilled linemen or repairmen. The possible faults include shorts, opens, and high impedance leakage paths between conductors.
It is another object of this invention to provide an apparatus and method having the above characteristics and which can perform the desired measurements for cables of varied configuration including a combination of individual conductors, twisted wire pairs, coaxial cables, individual or multiconductor shielded wires, etc.
It is a further object of this invention to provide an apparatus as described above which is compactly constructed and readily portable.